A plurality of electrochemical cells are connected together to form a battery. Silver-containing material is widely used as a cathode material in electrochemical cells. Silver-containing cathodes typically contain silver carbonate, silver thiocyanate, divalent silver oxide, silver bismuth oxide, copper silver vanadium oxide, and silver vanadium oxide. Some batteries, when using some of these compounds as the cathode material in individual electrochemical cells therein, however, do not exhibit ideal electrical properties. Ideal electrical properties include a low internal discharge rate (i.e., low increase in internal resistance over lifetime of the cell). A high internal discharge rate undesirably decreases the deliverable capacity (i.e., the integral of current times the discharge time) of a cell. Different cathode materials contribute to different problems. For example, silver chromate undesirably contributes to a large voltage drop during high loads. Divalent silver oxide is soluble and undesirably decomposes over time. These are just a few of the problems associated with some of the above-mentioned cathode materials.
Silver vanadium oxide (SVO) is utilized as a cathode material in lithium (Li) anode electrochemical cells (and, thus, batteries incorporating such electrochemical cells) due to its relatively high volummetric energy density (i.e., the product of capacity times average voltage divided by volume of material), which is particularly desirable for small batteries. The size of the battery is important in implantable medical devices, such as implantable cardiac defibrillators, as illustrated in FIG. 1, so that the device itself occupies a smaller volume within a patients body and is lighter in weight.
SVO is capable of being synthesized using a variety of methods. Methods of synthesis generally fall within two categories, depending on the type of chemical reaction that produces the SVO. SVO can be synthesized using a decomposition reaction, resulting in decomposition-produced SVO (DSVO). Decomposition reactions are known to utilize decomposable metal compounds, such as nitrates, nitrites, carbonates, and ammonium salts for the reacting metal components. A conventional DSVO reaction proceeds from silver nitrate and vanadium pentoxide according to the following reaction: 2 AgNO.sub.3 +2 V.sub.2 O.sub.5 .fwdarw.Ag.sub.2 V.sub.4 O.sub.11 +2NO.sub.x. Many conventional DSVO reactions, including the above-mentioned reaction, are not desirable due to the by-products that they produce, such as No.sub.X, which is toxic at certain levels.
Alternatively, SVO can be synthesized using a combination reaction, resulting in combination-produced SVO (C--SVO). C--SVO is characterized by a more crystalline structure, which, when compared to DSVO, contributes to its superior electrical performance in electrochemical cells. Many different silver-containing compounds have been used as reactants in such combination reactions, including AgVO.sub.3, Ag.sub.2 O, and Ag(0). A conventional C--SVO reaction proceeds at a temperature of about 500 degrees Centigrade from silver oxide and vanadium pentoxide according to the following reaction: Ag.sub.2 O+2 V.sub.2 O.sub.5 .fwdarw.Ag.sub.2 V.sub.4 O.sub.11, as described in U.S. Pat. No. 5,221,453 (Crespi). Crespi also discloses the use of flowing oxygen (O.sub.2) gas and Ag(0) according to the following combination reaction: 2 Ag+2 V.sub.2 O.sub.5 +0.5 O.sub.2 .fwdarw.Ag.sub.2 V.sub.4 O.sub.11. Flowing O.sub.2 was used to produce C--SVO having superior electrical performance as compared to CSVO produced in the presence of flowing or stagnant (i.e., having no active gas flow) air. The need for flowing O.sub.2, however, requires the use of a sealed retort, a tank of pure oxygen, and a flowmeter, all of which add expense to the synthesis process. Thus, there is a need to reduce the expense associated with the synthesis of SVO, while providing a material that exhibits superior electrical performance when used as a cathode in an electrochemical cell.
Table 1 below lists documents that disclose information of interest to methods of preparation of silver vanadium oxide (SVO) and electrochemical cells containing SVO cathodes, as well as electrochemical cells in general.
TABLE 1 ______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 4,016,338 Lauck April 5, 1977 4,158,722 Lauck et al. June 19, 1979 4,310,609 Liang et al. Jan. 12, 1982 4,391,729 Liang et al. July 5, 1983 4,542,083 Cava et al. Sept. 17, 1985 4,675,260 Sakurai et al. June 23, 1987 4,751,157 Uchiyama et al. June 14, 1988 4,751,158 Uchiyama et al. June 14, 1988 4,803,137 Miyazaki et al. Feb. 7, 1989 4,830,940 Keister et al. May 16, 1989 4,964,877 Keister et al. Oct. 23, 1990 4,965,151 Takeda et al. Oct. 23, 1990 5,194,342 Bito et al. March 16, 1993 5,221,453 Crespi June 22, 1993 5,298,349 Takeuchi March 29, 1994 5,389,472 Takeuchi et al. Feb. 14, 1995 5,439,760 Howard et al. Aug. 8, 1995 5,545,497 Takeuchi et al. Aug. 13, 1996 5,458,997 Crespi et al. Oct. 17, 1995 5,472,810 Takeuchi et al. Dec. 5, 1995 5,498,494 Takeuchi et al. March 12, 1996 5,498,495 Takeda et al. March 12, 1996 5,512,214 Koksbang April 30, 1996 5,516,340 Takeuchi et al. May 14, 1996 5,558,680 Takeuchi et al. Sept. 24, 1996 5,567,538 Oltman et al. Oct. 22, 1996 ______________________________________ Leising et al., Chem. of Materials, 5, 738-42 (1993) Zandbergen et al., Journal of Solid State Chemistry, 110, 167-175 (1994)
All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and Claims set forth below, many of the devices and methods disclosed in the documents in Table 1 may be modified advantageously by using the teachings of the present invention.